Mobile communication devices (i.e., mobile stations) are associated with a home network. For example, a mobile telephone is associated with a particular mobile provider with which the owner of the mobile telephone has subscribed for service. The home network manages the subscriptions and credentials of the mobile communication devices. When a mobile communication device is outside of the coverage area of the home network, the mobile communication device can receive services via a roaming or visited network. As part of accepting a mobile station, the roaming network communicates with the home network of the mobile station to verify the credentials of the mobile communication device owner and to verify that the home network will compensate the roaming network for the usage by the mobile communication device.
Home network operators have preferences regarding which roaming networks their subscribers utilize. For example, when a mobile communication device is roaming in a country in which the home network does not provide service, two roaming networks may be available and the home network may have an interest in the mobile communication device connecting to particular one of the roaming networks. For example, the home network may have a contractual agreement with the particular one of the roaming networks. The roaming network preferences of the home operator (in terms of a PLMN (Public Land Mobile Network) identity and access technology combination) are stored in priority order in the EFOPLMNwACT (Operator controlled PLMN selector with Access Technology) data file in the subscriber identity module (SIM) (described in Section 4.2.53 of 3GPP TS 31.102). This list is used in automatic network selection of a roaming network (as described in Section 4.4.3.1.1 of 3GPP TS 23.122).
Another method for a home network to direct a mobile communication device to a desired roaming network is called Steering of Roaming, and is described in Section 4.4.6 of 3GPP TS 23.122. According to the steering operation, the EFOPLMNwACT (Operator controlled PLMN selector with Access Technology) data file in the subscriber identity module (SIM) of a mobile communication device can be updated through the use of a USAT REFRESH command qualifier (as described in 3GPP TS 31.111) of type “Steering of Roaming”, and a new scan is triggered. The mobile communication device then uses the updated priority list when selecting a roaming service provider.
When in a visited network, a mobile station periodically scans to identify available networks within range of the mobile station. The results of the scan may cause the mobile station to change its connection from a first visited network to a second visited network if the second visited network has a higher priority than the first network according to the EFOPLMNwACT.